1. Field of the Invention
The present invention relates to solar power production, and more particularly, to solar receiver panels for use in solar boilers.
2. Description of Related Art
Solar power generation has been considered a viable source to help provide for energy needs in a time of increasing consciousness of the environmental aspects of power production. Solar energy production relies mainly on the ability to collect and convert energy freely available from the sun and can be produced with very little impact on the environment. Solar power can be utilized without creating radioactive waste as in nuclear power production, and without producing pollutant emissions including greenhouse gases as in fossil fuel power production. Solar power production is independent of fluctuating fuel costs and does not consume non-renewable resources.
Solar power generators generally employ fields of controlled mirrors, called heliostats, to gather and concentrate sunlight on a receiver to provide a heat source for power production. A solar receiver typically takes the form of a panel of tubes conveying a working fluid therethrough. Previous solar generators have used working fluids such as molten salt because it has the ability to store energy, allowing power generation when there is no solar radiation. The heated working fluids are typically conveyed to a heat exchanger where they release heat into a second working fluid such as air, water, or steam. Power is generated by driving heated air or steam through a turbine that drives an electrical generator.
More recently, it has been determined that solar power production can be increased and simplified by using water/steam as the only working fluid in a receiver that is a boiler. This can eliminate the need for an inefficient heat exchanger between two different working fluids. This development has lead to new challenges in handling the intense solar heat without damage to the system. One such challenge is the fact that in typical fossil fuel boilers, heating occurs all around much of the boiler tubing and thermal expansion is uniform, but in solar boilers the heating is typically all on one side of the boiler panels. In typical fossil fuel boilers, water wall tubes often are arranged having heating primarily on only one side, however, in solar boiler applications, heat flux or heat input is at a greater concentration and typically has exclusively one sided heating for all systems. A temperature gradient of up to about 300° F. can exist across the thickness of a solar boiler panel. This one-sided heating causes significant thermal expansion on the heliostat side of boiler panels while the reverse side, which is typically insulated, experiences significantly less expansion. The difference in thermal expansion on the two sides of boiler panels makes solar boiler panels tend to bow outward and can create stresses in the boiler tube panels. Moreover, since solar boilers operate on a daily cycle, the stresses due to thermal expansion gradients can become the basis for fatigue failure.
One approach that has been used to address this problem is to support the panels from the bottom using supports that hold the panel from bowing in the middle, but allow for vertical movement. Such methods as are known are typically complicated in terms of installing, removing, and replacing panels from the supports. Additionally, systems that support boiler panels from the bottom require special plumbing to account for the fact that the top of the panels move due to thermal expansion, which is opposite of typical boiler configurations.
While the known systems of solar power production have generally been considered satisfactory for their intended purposes, there has remained a need in the art for supporting solar receiver panels in solar boilers that can accommodate thermal expansion while alleviating undue stress that could otherwise lead to failure. There is also a need for such a support system that accommodates easy installation, removal, and replacement of boiler panels. The present invention provides a solution to these problems.